In New York City, where the study was conducted, asthma among school-age children ranges from a low of 3% to a high of 19%, depending on neighborhood, and even children growing up within walking distance of each other can have a two- to threefold difference in risk. The researchers pinned the differences on airborne black carbon—soot—which comes mainly from incomplete combustion by diesel trucks and oil furnaces. They found that black carbon levels were high in homes of children with asthma. They also reported elevated levels of black carbon within homes in neighborhoods that had high asthma prevalence, and high densities of truck routes or homes burning low-grade or "dirty" heating oil.

The study may be the first to show an association between airborne soot in the home and proximity to buildings burning low-grade, dirty oil (technically known as types 4 and 6). Based on suspicions about the effects of soot, New York City is already moving to phase out use of low-grade oils, but the study could lend more urgency to the effort. "Because of its history as a shipping and oil refining center, New York City burns more dirty oil for residential and commercial heating than any other city in the country," said study coauthor Steven Chillrud, a research professor at the university’s Lamont-Doherty Earth Observatory. "These fuels produce more byproducts of incomplete combustion than cleaner oil or natural gas, and contribute substantially to air pollution. Buildings that burn dirty oil are unevenly distributed throughout the city, which could help explain disparities in health."

"This study adds to the evidence that further public health interventions on oil and truck emissions standards and the use of dirty oil may be warranted. This is especially timely as New York City considers regulations to further reduce the burning of low-grade oil for domestic heating," said the study's senior author, Matthew Perzanowski, an associate professor of environmental health at the university's Mailman School of Public Health.

The researchers collected air samples from inside the homes of 240 7- and 8-year-old children from middle-income neighborhoods throughout the city. These children also took breathing tests to measure exhaled nitric oxide, an indicator of lung inflammation.

"Airway inflammation plays an important role in the development of asthma, and can contribute to more frequent symptoms among children with the disease," said study lead author Alexandra Cornell, who teaches pediatrics at Dartmouth Medical School and previously was a fellow at Columbia University Medical Center/New York-Presbyterian Hospital. "That this increased risk comes from air pollution lends weight to New York City's efforts to improve air quality, including phasing out the use of dirty oil, which is a large contributor to local air pollution.”

The study was funded by the U.S. National Institute of Environmental Health Sciences and the U.S. Environmental Protection Agency.